Method and apparatus for retreading tires

ABSTRACT

The invention is a method and apparatus for bonding and shaping retread stock to a tire casing. A pair of circumferentially mating mold elements engage the tread area of a tire to be retreated. The molds are divided along a horizontal mating plane and are supported in aligned relationship within a pair of substantially hemispherical pressure chamber members adapted for closing and opening about the tire. Centering plates are provided to locate the tire concentrically within the mold and to form an internal pressure chamber within the tire. The internal pressure chamber is pressurized forcing the tire against the mold elements. Subsequently the outer chamber or chambers are pressurized to a pressure equal to the internal pressure. The centering or bead plates are then displaced from engagement with the tire. Heat is applied for bonding and shaping the tread stock to the tire casing. In another embodiment, elastomeric diaphragms are used as mold elements and the bead plates remain stationary relative to one another. In still another embodiment, a combination of metal matrices and elastomeric diaphragms are used as mold elements.

United States Patent [191 Barefoot June 11, 1974 METHOD AND APPARATUSFOR RETREADING TIRES Related US. Application Data [62] Division of Ser.No. 52,534, July 6, 1970.

[52] US. Cl. 156/394, 156/96, 156/128 R, 156/394 FM, 264/36, 264/315,264/326,

[51] Int. Cl. B29h 5/04, B29h 17/36 [58] Field of Search 156/96, 110,123, 126-130, 156/394, 399 FM; 264/36, 315, 316, 326;

[56] References Cited UNITED STATES PATENTS 2,282,580 5/1942 Hawkinson156/96 2,292,286 8/1942 Owen 156/96 2,459,757 l/1949 Smith 156/962,903,742 9/1959 Barefoot 425/19 2,987,770 6/1961 Powell 4.25/233,184,794 5/1965 Sherkin 425/19 3,236,709 2/1966 Carver 156/96 3,240,6533/1966 Mattox et al7 156/96 3,397,099 8/1968 Barefoot 156/96 3,590,4337/1971 Rawls 425/19 3,745,084 7/1973 Schclkmann 156/394 PrimaryExaminer-C]ifton B. Cosby Assistant Examiner,1ohn E. Kittle A Home), Agent, or Firm Owen & Owen; Richard D.

[57] ABSTRACT The invention is a method and apparatus for bonding andshaping retread stock to a tire casing. A pair of circumferentiallymating mold elements engage the tread area of a tire to be retreated.The molds are divided along a horizontal mating plane and are supportedin aligned relationship within a pair of substantially hemisphericalpressure chamber members adapted for closing and opening about the tire.Centering plates are provided to locate the tire concentrically withinthe mold and to form an internal pressure chamber within the tire. Theinternal pressure chamber is pressurized forcing the tire against themold elements. Subsequently the outer chamber or chambers arepressurized to a pressure equal to the internal pressure. The centeringor bead plates are then displaced from engagement with the tire. Heat isapplied for bonding and shaping the tread stock to the tire casing.

In another embodiment, elastomeric diaphragms are used as mold elementsand the bead p1ates remain stationary relative to one another.

In still another embodiment, a combination of metal matrices andelastomeric diaphragms are used as mold elements.

11 Claims, 14 Drawing Figures mmamuu 11 2914 3816121 7 SHEET 1 OF 7PATENTEDJun 1 1 I914 SHEET 30F 7 PATENTEBJun 1 1 m4 SHEET 50F 7 METHODAND APPARATUS FOR RETREADING TIRES BACKGROUND OF THE INVENTION Thisinvention relates to a method and apparatus for retreading tires. Priorart apparatus generally included mold forms which enclosed a portion ofa tire casing. An inner curing tube, which consisted of an air-filledtube, was positioned within the apparatus to force the tire casingagainst the mold. In addition, a collapsible metallic curing rim waspositioned within the tire over the curing tube. In an alternativemethod, a road type curing rim was used to directly hold the beadsduring curing. Such apparatus while being effective in reforming thetread area of the tire, often resulted in malforming the tread area. Theroad type rim often restricted the tire from assuming a correct positionwithin the tire matrix. In addition, many sizes of curing rims wereneeded to handle various tire sizes.

The present invention contemplates reforming tread areas of tires at amuch faster rate with a minimum of distortion of the bead and sidewallareas of the tires.

SUMMARY OF THE INVENTION The present invention comprises a retreadingmethod and apparatus which is much faster to use; eliminates the needfor curing rims; and reduces overstretching and buckling of the tirecord bodies.

A tire casing including attached tire stock is positioned within matinghalves of a matrix. A pair of opposed bead plates initially engage andsupport the tire beads and also form part of an inner air chamber withinthe tire casing.

Upper and lower shells surround the matrix and form an autoclave havingan exterior pressure chamber adjacent the bead portionsof the tirecasing. Preferably, the section of the autoclave adjacent the treadportion of the tire is initially vented to atmosphere or a reducedpressure area so that air entrapped between the tire casing and thematrix may be removed.

The inner chamber is pressurized, forcing the tread area and tread stockclosely against the matrix. The exterior chambers are then pressureduntil they equal the pressure of the inner chamber. The bead plates aremoved away from the tire heads when the chamber pressures aresubstantially equal allowing the beads to float to a static condition.

Heating means, comprising electrical resistance heaters, steam, heatedair, hot water or a combination of these means, are then energized oractivated to cure the retread stock.

One of the objects of this invention is to provide a mechanismcomprising a horizontally divided pressure chamber having a verticallymovable upper portion adapted for sealing contact along a commondividing line against a stationary lower portion, and upper and lowermold elements associated respectively with the pressure chamber portionswherein a band of retread stock may be bonded and shaped to theperiphery of a tire casing positioned within the mold elements after thechamber is closed and sealed.

Another object of this invention is to provide a pair of axially alignedcentering or bead plates adapted to engage the bead portions of the tireand effectively Iocate the tire within the chamber to facilitate itscentral positioning within the mold halves during their enclosure aboutthe tire.

Another object is to provide a mechanism for moving the bead platesaxially relative to the tire to permit engagement of the outer edges ofthe plates with the inner edges of the beads of the tire to define aninner pressure chamber to permit disengagement of the plates from thebeads to free this beads and sidewalls of the tire from extraneousrestraint during the cure.

Another object is to provide exterior pressurized chambers adjacent thebead areas of the tire casing pressured to the pressure of the innerchamber.

Another object is to provide apparatus which correctly centers the tirecasing and tread stock during the retreading operation.

Another object is to provide means within the chamber adapted tofacilitate use of molds of varying depths and diameters to accommodatethe retreading of tires of various sizes.

Another object is to provide a supply of heat to the molds for curingthe retread stock to the tire casing.

Another object is to provide a supply of fluid pressure within the innerchamber and within the tire to compact the retread stock against thecontours of the mold and to compact the tread area of the tire againstthe retread stock to facilitate a uniform bonding.

Another object is to provide mechanism for raising and lowering of theupper autoclave shell and the upper half of the matrix and for raisingand lowering the bead plates.

Another object is to provide a pressure regulating and control means tovary the fluid pressures within the tire and within the chamber duringthe retreading operation.

Another object is to provide a mold comprising a novel flexiblediaphragm means for constraining a tire casing and applied preformedtread stock without the use of a metallic matrix.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical cross-sectionalview with parts broken away showing one embodiment of retreadingapparatus according to my invention, with a tire to be retreaded beingsupported on bead plates;

FIG. 2 is a vertical cross-sectional view with parts broken away andwith the mold parts and chamber elements of FIG. 1 shown in a closedposition;

FIG. 3 is a cross-sectional fragmentary planview taken along the line3-3 of FIG. 2;

FIG. 4 is a fragmentary vertical cross-sectional view of the FIG. Iapparatus with the centering or bead plates separated and removed fromcontact with the tires and with the molds closed in bonding and shapingposition on the tire;

FIG. 5 is a fragmentary vertical cross-sectional view of a portion ofthe FIG. I apparatus on a slightly enlarged scale;

FIG. 6 is a fragmentary cross-sectional plan view taken along the line6--6 of FIG. 5;

FIG. 7 is a plan view of the FIG. I apparatus showing the clamping ringin its disengaged position;

FIGS. 8 and 9 are plan and elevational views respectively of a toggledevice adapted for locking the clamping ring;

FIG. is a detail plan view of a fastening device arranged for securingone of the bead plates to a telescopic center post;

FIGS. 11 and 12 are fragmentary vertical crosssectional views of anotherembodiment of the present invention in which a pair of flexible upperand lower diaphragms are utilized; and

FIGS. 13 and 14 are fragmentary vertical crosssectional views of stillanother embodiment of the present invention, particularly adapted toretreading both the tread area and a portion of the sidewall of a tire.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 to 6, oneembodiment of the invention comprises upper and lower shells 20, 21,having mating edges 22, 23, which may be brought to gether into conjointrelationship to form an autoclave chamber 24 as indicated in FIGS. 2 and5. The upper shell is providedwith arms 25, which extend outwardly andare connected to a pair of piston rods 26 of pneumatic cylinders 27.

The lower shell 21 is provided with a pair of arms 28 which extendoutwardly from the shell 21. The cylinders 27 are mounted on the arms28. The lower shell 62 mounts a spring biased locking clamp 64 (seeFIG..

21 is provided with a plurality of legs 29 which are welded or otherwisesecured to a platform 30 which in turn may be mounted on a base 31. Theplatform 30 serves as a support for certain parts of the apparatusactuating mechanism to be described below.

The upper arms 25 extending from the'upper shell 20 mount a pair ofdepending racks 32, the teethof which are in mesh with a pair of piniongears 33 which are keyed to the ends of a transverse shaft 34. The shaft34 is carried in bearing blocks 35 which are mounted on brackets 36 offramework 37 secured to the legs 29. The framework 37 also carries abracket 38 which is fitted with a fulcrum pin 39 to which a yoked lever40 is hinged.

The lower shell 21 is fitted with a center collar 41 which provides acenter guide for an axially movable tubular column 42. A packingassembly 43 is bolted to the center collar 41. At the upper end of thecolumn 42 there is affixed a circular bead plate 44 having aperipherally extending lip 45 adapted to engage the lower bead 46 of atire 47 to be retreaded. The plate 44 acts as a centering means and as aleveler for the tire and as a portion of an inner pressure chamber.

The column 42 is affixed at its lower end to a coupling 48 extendingfrom a vertically movable'pneumatic cylinder 49 mounted above theplatform 30. The

cylinder 49 is carried on trunnion pins 50 mounted on the yoked lever40. The lever 40 mounts a thrust pin 51 between the coupling 48 andthefulcrum bracket 38.

- A clevis 52 mounted on the upper end of a piston rod which extendsupwardly from the platform 30. Slots 56 (see FIG. 1) are formed in theyoke lever 40 topermit relative drift of the trunnion pins 50 duringvertical movement of the column 42.

The cylinder 54 is provided with pneumatic feed lines 57, 58 which areutilized in vertically moving the col-' umn 42 and the attached beadplate 44.

The cylinder 49 includes a piston 59 and double extending piston rods60, 61. The rod 60 extends through the coupling 48 and the telescopiccolumn 42 to a height above the plate 44. An upper centering or beadplate 62 is mounted on the upper end of the rod and engages the upper oropposite bead 46a of the tire 47. The plate 62 is provided with anopening 63 to permit vertical slidable engagement with the rod 60. Theplate 10) having a central recess portion 65 adapted to engage a groove66 near the upper end of the rod 60.

An adjustment screw at the lowermost end of the rod 61 (see FIG. 2)'isused when matrices of a different width are placed in the autoclave 24to insure correct vertical centering of the bead plates 44 and 62. Thelower piston rod 61 is adapted to pass downwa'rdly from the piston 59through a coupling 67. A spacer sleeve 68 is positioned below thecoupling 67 and correctly centers the bead plates 44 and 62 when theyare in the curing position. The adjustment screw 70 having a. lock nut71 is adapted to engage the base 30. The adjustment is utilized toadjust the position of the bead plates 44 and 62 to insure that thehorizontal centerline of the plates 44 and 562 is identical with theparting line or horizontal centerline of the matrix when the plates 44and 62 are in their curing position.

The sleeve 68 also limits the travel of the cylinder 49 and of the lowerbead plate 44 when the plates 44 and 62 are moved to their openposition.

The cylinder 49 is provided with pneumatic feed lines 72, 73 (.seeFIG. 1) which are utilized to move the piston 59, rod 60 and centeringplate 62 vertically. v

The shells 20, 21 are provided with horizontally disposed annularlyshaped mold mounting plates 74, 75 (see FIG. 5). The plates 74, 75 areadapted to support a pair of tire mold elements or matrix halves 76, 77in a substantially horizontal position and in concentric alignment withthe bead plates 62, 44 respectively. The matrix halves have annularoffset shoulders 78 and 79 to facilitate diametrical alignment of themolds at their parting line. The facing edge 23 on the lower autoclaveshell 21 is provided with a groove 80 and suitable 0 ring seal 81..Themounting plates 74, 75 are fitted with replaceable spacer shims 82, 83to accommodate molds of various heights. The shims 82, 83 may be adaptedfor adjustment radially on the plates 74, 75 to accommodate molds ofvarious diameters.

Venting bands 84 and 85 are mounted on the upper and lower matrix halves76, 77 respectively. Vent lines 86 are connected to the bands 84 and 85.The vent lines 86 communicate with the atmosphere.

The perimeters of the matrix halves 76, 77 are provided, with vent holes87, 88, respectively, which are designed to permit escape of air thatwould otherwise be entrapped within the molds when they are enclosedabout a tire. The entrapped air thus may pass outwardly through thevents 87, 88 into the venting bands 84 and 85 which surround the moldelements 76,77.

In another embodiment the bands 84 and 85 are not provided. Rather, theentrapped air is passed outwardly through the vents 87 and 88 into anannular space 89 surrounding the mold elements 76, 77. The space 89 isat a lower pressure. Prior to pressurizing the space 89 (as discussedbelow) retread stock is forced into the vent holes 87, 88 and at leastpartially cured. This closes the vent holes 87, 88 and prevents air fromentering the vent holes 87, 88 during pressurizing of the space 89.Preferably, a valve 90 is provided on the vent lines 86.

In the above embodiment, the space 89 is a part of an exterior chamberdefined by the shells 20 and 21. In still another embodiment (notshown), seals are provided to separate the space 89 from exteriorchambers in the shells 20 and 21. In this embodiment the space 89 isvented and preferably valved to atmosphere.

According to the present method, a tire to be retreaded is cleaned andbuffed, minor blemishes are repaired, and much of the old original treadis removed and trimmed to a predetermined line to present a smoothperipheral surface upon which the retread stock is affixed. A coating ofadhesive is applied to the periphery of the tire and tread stock isadhered to the tire casing. Various devices are available commerciallyfor applying retread stock to a tire.

In accordance with the present invention, the upper plate 62 is firstremoved from its locked position on the rod 60 by opening the springbiased locking clamp 64.

The tire casing 47, with a layer of retread stock 47a attached, isplaced over and is supported by the lower centering bead plate 44. Theplate 44 is provided with a port 91. A conduit 92 extends'between anentrance collar 93 fixed to the wall of the lower shell 21 and the port91. A valve (not shown) is provided to control fluid pressures.Initially, air of an inflating pressure is introduced through the port91 and the upper bead plate 62 is pushed axially downwardly along therod 60 until an air seal is formed and an inner air chamber A, definedby the upper and lower bead plates 44, 62 and the tire casing 47, beginsto be pressurizedQWhen theupper bead plate reaches the position shown inFIG. 1,

the clamp 64 snaps into the locked position.

Referring to FIG. 1, during the initial step, the rod 60 is moved to itsextreme upper position. The bead plates 44 and 62 are at their maximumspacing. As shown in FIG. 1, this reduces the outer circumference of thetire casing 47 to enable easy seating of the tire casing 47 within thelower matrix 77.

The inflated tire 47 is next lowered into contact with the mold half 77.Pressure is admitted to the cylinder 54 through the conduit 58 therebylowering the lever 40, and the cylinder 49 associated therewith. Thissimultaneously lowers the column 42, rod 60 and plates 44, 62. Cylinders27 are actuated to bring the upper shell 20 and upper matrix 76downwardly to enclose the tire. The shoulder 78 is brought into registerwith the shoulder 79 to properly align the mold halves. The mating edges22, 23 are likewise brought into correct alignment. A removable clampring 96 (see FIGS. 7-9) is provided for securing the matrix halvesagainst separation. A toggle device 97 is provided to facilitateapplication and removal of the clamp ring 96. Pressure is then admittedthrough conduit 72 into the cylinder 49 thereby lowering the centeringplate 62 to a correct vertical spacing with the lower plate 44 (see FIG.4).

With the shells 20, 21 and the matrix halves 76, 77 closed about thetire 47, additional fluid pressure, for

example 150 p.s.i. air, is admitted to the interior of the In thisembodiment, after a short period of time auxiliary fluid pressure isintroduced to a space 100 in the upper shell 20 through a fluid conduit101 having an entrance collar 102. Similarly, fluid pressure isintroduced in a communicating lower space 103 through a conduit 104having an entrance collar 105. The pressure inside the unitary exteriorchamber consisting of spaces 89, 100 and 103 is increased to an amountsubstantially equal to the pressure within the interior chamber A. Atthis time, the plates 44 and 62 are separated as shown in FIG. 4.

When the supporting or bead plates 44 and 62 are removed from the beadareas of the tire 47, the beads are free to move to a static condition.It has been found that the tire beads have a memory and move to acorrect bead positioning.

While the interior and exterior chambers are normally pressurized to 150p.s.i., it has been found that this pressure may vary. The normal rangeis between 100 p.s.i. and 300 p.s.i. Pressures below 100 p.s.i. normallydo not force the tire tread areas tightly against the matrix whilepressures above 300 p.s.i. tend to permeate through the tire unless anair barrier layer is positioned along the inside wall of the tirecasing;

Sufficient heat is then applied to cure the tire 47. The heating meansmay be, for examples, electrical resistance heating elements, heatedair, or steam. In the present embodiment, heat is supplied by steamconduits 98, 99 which communicate with passages formed in the matrixhalves. Normally, the curing temperature is between 275 and 325 F. Ithas been found that the total curing time using the method and apparatusaccording to the present invention is reduced significantly.

During curing, the tire is subjected to a relatively intense pressure inthe tread area while the bead areas and sidewall areas of the tireadjacent the tread are subjected to little orno deformation from theprocedure.

The pressure within the autoclave chamber 24 is then reduced toatmospheric. The toggle device 97 is released to permit removal of theclamp ring 96 from the mating edges of the shells 20 and 21.

' Fluid pressure is introduced at the lower ends of the fluid cylinders27 through conduits 106. The rods 26 associated with the cylinders 27raise the upper shell 20 from contact with the lower shell 21. Theretreaded tire 47 is then removed and the above procedure is repeated.

Another embodiment of the invention is shown in FIGS. 11 and 12. In thisembodiment an annular band of stock having a preformed tread is cementedto the perimeter of a tire carcass and is vulcanized to the tire casingwith pressure and heat. In the present apparatus, the metal matrix iseliminated and an elastomeric diaphragm is used.

The present embodiment includes an autoclave comprising a pair of upperand lower shell members 111 and 112 which cooperate with a flexiblepartitioning means and with fixed bead plates to form upper and lowersealed pressure chambers 113 and 114.

Tire centering rings 115 and 116 having shaped edges 117 adapted toengage the bead 118 of a tire I 19 are provided. The upper ring 115 issecured by means of screws 120 to a supporting plate 121 which is boltedto a post 122 affixed to the shell 111.

The shells 111 and 112 are provided with upper and lower mating surfaces123 and 124, respectively, adapted to form a pressure tight seal whenclosed. A clamp ring 960 is provided to preclude separation of theshells 111 and 112 while they are closed and subjected to internalpressure.

A circumferential groove 126 is defined along the lower edge of theshell 1 1 1 and receives an annular diaphragm 127. The diaphragm 127 isconstructed of a rubberized or other type of flexible material, forexample, a resin coated nylon fabric, and together with the bead plate121 and shell 1 11 defines the chamber 113. The diaphragm 127 isprovided at its outer perimeter with an upturned shoulder portion 128which is cemented or otherwise secured in the groove 126. The innerperimeter of the diaphragm 127 is similarly configurated with a shoulderportion 130 which may be clamped into interlocking engagement betweenthe periphery of the ring 115 and a lip 131 extending along the edge ofthe supporting plate 121.

Fluid pressure may be regulated to and from the pressure chamber 113through a pressure conduit 132, 3-way valve 133 and an entrance collar134 extending into the chamber through the shell 111.

A second flexible annular diaphragm 135 is provided to form a closureportion of the chamber 114. The outer perimeter of the diaphragm 135 hasa down turned shoulder portion 136, which may be cemented or otherwisesecured in a groove 137 formed in the mating face of the shell 112. Theinner perimeter of the diaphragm 135 is provided with an upturnedshoulder portion 139 adapted to be clamped by a plurality of screws 140into interlocking engagement between the periphery of the lower ring 116and a lip 141 extending along the peripheral edge of a lower supportingplate 142.

The plate 142 is welded or otherwise affixed to a tubular column 42a andis in vertical sliding engagement with a guide collar 41a mounted in thelower portion of the shell 112. The plate 142 may be raised and loweredwithin the chamber 114 by the action of a lever a, trunnion pins a,thrust pin 51a, pneumatic cylinder 54a, and other associated parts asdisclosed above.

It has been found that in some situations where high pressures are usedand where the tire casing is permeable, it is-desirable to use apressure tube (not shown) within the tire casing. lnv this embodiment,mating backing members (not shown) extend from the rings and 116 andserve as a stop for the pressure tube to prevent the tube from spreadinginto the center of the tire casing rather than applying force on thetire body for the vdiaphragms 127 and to press against.

Fluid pressure is supplied and regulated to and from the lower exteriorpressure chamber 114 through a pressure conduit 143, 3-way valve 144 andentrance collar 145 which extends through the shell 112. The shell 112is mounted on a plurality of legs 29a and is provided with arms 28a towhich pneumatic cylinders 27a are affixed.

The shell 111 has outwardly extending arms 25a which are connected topiston rods 26a for imparting vertical movement to the shell 111.

In operation, a tire 119 has applied thereto by cement or otherfastening means a strip of preformed retread stock 146, and is placed ina restive position on the lower centering plate 142, the lowermost ofthe beads 118 of the tire engaging the lip 117 on the lower ring 116.

The cylinders 27a are then activated to lower the shell 111 intoengagement with the shell 112. The clamp ring 960 is then locked aroundthe mating edges of the shells. The edges 128 and 136 of the diaphragms127 and 135 are thereby held against disengagement from the shells (seeFIG. 12). The upper and lower plates 121 and 142 are brought intocontact with the tire beads 118 to form an inner pressure chamber 147within the tire 119.

Fluid pressure of approximately 125 p.s.i. is introduced into thechamber 147 through an opening 148, a semi-rigid conduit 149, and anentrance collar 150 in the shell 1 12. A 3-way valve 151 or other meansis provided toregulate the fluid pressure introduced into the chamber147 within the tire. The degree of pressure introduced will dependlargely on the type, size and quality of the tires being retreaded andwill vary from 50 to 250 p.s.i. Simultaneously, the pressures in thechambers 113 and 114 are increased by introducing fluid under pressurethrough the conduits 132 and 143, thereby forcing the diaphragms 127,135 into intimate and forceful contact exterior of the tire 119 andtread stock 146 as shown in FIG. 12.

The diaphragm 135 is provided with an outlet passage 153 connected to asemi-rigid conduit 154. The conduit 154 leads to an entrance fitting 155mounted in the shell 1 12. Air which becomes entrapped between thediaphragms 127 and 135 as they are brought together to enclose the tire,may be withdrawn by suction means (not shown) through the conduit 154,or may be exhausted to the atmosphere. Fluid pressures within thechambers 113 and 114 and within the inner tire chamber are increased insubstantially equal amounts to approximately 125 p.s.i. The tread stock146 is thereby forcibly pressed against the perimeter of the tire,which, conversely, is pressed outwardly with an equal force. Thisrelatively high pressure is maintained for a sufficient time period toinsure. bonding of the tread stock to the tire. Heating means, forexample electrical resistance heaters 156, are positioned in thechambers 113 and 114 to raise the temperature within the chambers toapproximately 200 to 300 F. during the bonding period. If desired, steamor other heating means (not shown) may be utilized.

Still another embodiment of the invention is shown in FIGS. 13 and- 14.In this embodiment retread" stock is placed not only on the tread areaof the tire, but also on the sidewalls. A pair of upper and lower shellmembers 157 and 158 mount upper and lower matrix halves 159 and 1611.Mold mounting plates 161, 162, and associated spacing plates 163 areprovided to position the matrix halves 159 and accurately within theshells 157 and 158. Upper and lower tire centering or bead plates 1.64and 165 are provided with outwardly extending lips or edges 166 adaptedto engage the inner or beaded edges 167 of a tire 168.

The upper bead plate 164 is provided with a threaded opening 169 adaptedto engage a threaded stem 170 on a vertically movable rod 60a of theapparatus.

The matrix halves 159 and 160 are provided with inwardly facingsubstantially vertical wall portions 171 which conform generally to thecontours of the tire being used. inwardly directed flange portions 172act to limit the final width of the tread and also to support at leastin part the sidewall structure or casing of the tire. A flexiblediaphragm 173 preferably of circular shape is adapted to enclose theotherwise open area extending across the diameter of the upper matrixhalf 159. The diaphragm 173 is provided with an upwardly directed rimportion 174 which engages and is preferably cemented into acircumferential groove 175 in the flange portion 172 of the upper matrixhalf 159.

The lower bead plate 165 is affixed, as by welding, to a verticallymovable sleeve 42a carried by the apparatus. Suspended below the plate165 and attached thereto is a collar 177 adapted to support the innerperipheral edge 178 of an annular diaphragm 179. The outer periphery ofthe diaphragm 179 is provided with a down turned rim portion 185 whichengages a circumferential groove 181 in the flange portion 182 of thematrix half 161).

The diaphragm 179 is adapted to enclose the otherwise open annular areaextending from the collar 177 outwardly to the flange portion 182 of thematrix half 160.

When the shells 157, 158 are brought into closed position, and thematrix halves 159 and 160 are enclosed about a tire, the diaphragms 173,179 will divide the space within the shells into first, an inner space183 (see FIG. 14) within the tire 168; secondly, an exterior chamber 184above the diaphragm 173 next to the shell 157; and thirdly, an exteriorchamber 185 below the diaphragm 1'79 and adjacent to the shell 158.

The tire initially is partially inflated through a fluid conduit 149while supported by the centering bead plates 164 and 165. The pressureis then increased to approximately 150 psi, forcing the tire 168 againstthe matrix halves 159 and 160. Vent openings 186 through the mold walls171 are provided to permit the escape of air entrapped between the tireand mold walls. Vent conduits 176 are provided to permit the escape ofair from between the diaphragms 173, 179 and the exterior surface of thetire casing. Vent band assemblies 187 are provided to conduct escapingair to the atmosphere.

During the initial loading, the bead plates 164 and 165 are moved totheir maximum spacing to reduce the maximum diameter of the tire andfacilitate the entry of the tire within the matrix halves 159 and 160.After the tire is properly seated, fluid pressure is simultaneouslyintroduced into the exterior chamber consisting of the spaces 184, 185through suitable fluid co nduits to counterbalance the fluid pressure inthe space 183.

The pressure in the three interior and exterior chambers is increased insubstantially equal amounts. When the pressures are balanced, the beadplates 164 and 165 are moved vertically toward each other allowing thebead 167 of the tire 168 to float freely until it has reached its staticcondition.

At this time, heating means are activated to raise the interior andexterior chambers to a curing or bonding temperature of between 250 to300 F. In the present embodiment, the heating means comprises a seriesof steam conduits 188 which communicate with passageways in the matrixhalves 159 and 160.

The diaphragms 173 and 179 support the sidewalls of the tire 168 duringthe retreading operation.

After curing, the fluid pressures in the exterior and interior chambersare released to atmosphere. The

shells 157, 158 are separated and the tire 168 removed from the mold.

What I claim is:

1. Apparatus for retreading tires comprising, in combination, a pair ofmating shell members, a mold element mounted in each of said matingshell members, said mold elements comprising rigid matrix halves andbeing adapted to receive a tire to be retreaded, a tire engaging andcentering means positioned Within said mating shell members, said theengaging and centering means and the tire defining an inner pressurechamber, means for pressurizing said inner pressure chamber, means fordefining at least one exterior pressure chamber in opposed relationshipto said inner pressure chamber and the tire, means for pressurizing saidexterior pressure chamber, and heating means for raising the temperaturewithin said mating shell members.

2. Apparatus according to claim 1, including means for opening theuppermost one of said mating shell members.

3. Apparatus according to claim 2, wherein said tire engaging andcentering means includes spaced bead plates and means for moving atleast one of said bead plates vertically relative to said other one ofsaid bead plates.

4. Apparatus according to claim 1, including means for raising andlowering the uppermost one of said mating shell members.

5. Apparatus according to claim 4, including means for moving at leastone of said bead plates vertically relative to said other one of saidbead plates.

6. Apparatus for retreading tires comprising, in combination, a pair ofmating matrix halves, said matrix halves being separable to receive atire casing and tread stock, a pair of opposed bead plates forsupporting the bead of the tire casing and for forming together with thetire casing an inner pressure chamber, means for moving said bead platesto non-force transmitting positions adjacent the tire casing, shellmeans positioned adjacent said bead support means for defining at leastone exterior pressure chamber adjacent the bead portions of the tirecasing, means for pressurizing such inner pressure chamber and saidexterior pressure chambers and means for heating said tire casing andsaid tread stock.

7. Apparatus according to claim 6, wherein said means for moving saidbead plates include a telescopic column assembly having an inner rod anda coaxial outer tube, said inner rod mounting one of said bead platesand said outer tube mounting the other one of said bead plates, firstcylinder means for vertically moving said telescopic column assembly andsecond cylinder means for moving said inner rod and said outer tubetoward and away from one another, whereby said bead plates are movedtoward and away from one another.

8. Apparatus according to claim 6, wherein said shell means compriseupper and lower mating shell members, and means for vertically movingsaid upper shell member toward and away from said lower shell member.

9. Apparatus according to claim 8, wherein said means for moving saidupper shell member comprises at least one cylinder operatively connectedto said upper shell member.

10. Apparatus according to claim 9, including guiding means for guidingthe movement of said upper shell 1 1 member comprising a pair ofvertical racks connected to opposed sides of said upper shellmember, atransverse shaft mounted adjacent said lower shell member, and opposedpinions mounted on said transverse shaft, each of said opposed pinionsengaging a respective one of said racks.

11. Apparatus for bonding and shaping a layer of retread stock to theperiphery of a tire, comprising a frame, a lower shell member mounted onthe frame, a lower mold element comprising a tread shaping portioncarried by the shell and adapted to shape a correlative portion of saidstock; an upper shell member adapted to cooperate with said lower shellmember to form a pressure chamber, an upper mold element comprising atread shaping portion carried by said upper shell adapted to shape acorrelative portion of said stock;

heating means for said molds; elevating means carried by said frameadapted to raise and lower said shell and said upper mold elementmounted therein; tire centering means mounted within said lower shellcomprising spaced apart plates adapted to be engaged and disengaged withbead portions of said tire; means to inflate said tire within saidchamber and within said molds and to expand said tread area of said tireagainst said molds; fluid exhaust means associated with said molds andwith at least one of said shells to permit removal of fluid from withinsaid molds while said tire is being inflated therein, thereby insuringsubstantially solid contact of the tread stock on said tire with theshaping portions of said molds, and means for pressurizing the areaexterior of said tire.

1. Apparatus for retreading tires comprising, in combination, a pair ofmating shell members, a mold element mounted in each of said matingshell members, said mold elements comprising rigid matrix halves andbeing adapted to receive a tire to be retreaded, a tire engaging andcentering means positioned within said mating shell members, said tireengaging and centering means and the tire defining an inner pressurechamber, means for pressurizing said inner pressure chamber, means fordefining at least one exterior pressure chamber in opposed relationshipto said inner pressure chamber and the tire, means for pressurizing saidexterior pressure chamber, and heating means for raising the temperaturewithin said mating shell members.
 2. Apparatus according to claim 1,including means for opening the uppermost one of said mating shellmembers.
 3. Apparatus according to claim 2, wherein said tire engagingand centering means includes spaced bead plates and means for moving atleast one of said bead plates vertically relative to said other one ofsaid bead plates.
 4. Apparatus according to claim 1, including means forraising and lowering the uppermost one of said mating shell members. 5.Apparatus according to claim 4, including means for moving at least oneof said bead plates vertically relative to said other one of said beadplates.
 6. Apparatus for retreading tires comprising, in combination, apair of mating matrix halves, said matrix halves being separable toreceive a tire casing and tread stock, a pair of opposed bead plates forsupporting the bead of the tire casing and for forming together with thetire casing an inner pressure chamber, means for moving said bead platesto non-force transmitting positions adjacent the tire casing, shellmeans positioned adjacent said bead support means for defining at leastone exterior pressure chamber adjacent the bead portions of the tirecasing, means for pressurizing such inner pressure chamber and saidexterior pressure chambers and means for heating said tire casing andsaid tread stock.
 7. Apparatus according to claim 6, wherein said meansfor moving said bead plates include a telescopic column assembly havingan inner rod and a coaxial outer tube, said inner rod mounting one ofsaid bead plates and said outer tube mounting the other one of said beadplates, first cylinder means for vertically moving said telescopiccolumn assembly and second cylinder means for moving said inner rod andsaid outer tube toward and away from one another, whereby said beadplates are moved toward and away from one another.
 8. Apparatusaccording to claim 6, wherein said shell means comprise upper and lowermating shell members, and means for vertically moving said upper shellmember toward and away from said lower shell member.
 9. Apparatusaccording to claim 8, wherein said means for moving said upper shellmember comprises at least one cylinder operatively connected to saidupper shell member.
 10. Apparatus according to claim 9, includingguiding means for guiding the movement of said upper shell membercomprising a pair of vertical racks connected to opposed sides of saidupper shell member, a transverse shaft mounted adjacent said lower shellmember, and opposed pinions mounted on said transverse shaft, each ofsaid opposed pinions engaging a respective one of said racks. 11.Apparatus for bonding and shaping a layer of retread stock to theperiphery of a tire, comprising a frame, a lower shell member mounted onthe frame, a lower mold element comprising a tread shaping portioncarried by the shell and adapted to shape a correlative portion of saidstock; an upper shell member adapted to cooperate with said lower shellmember to form a pressure chamber, an upper mold element comprising atread shaping portion carried by said upper shell adapted to shape acorrelative portion of said stock; heating means for said molds;elevating means carried by said frame adapted to raise and lower saidshell and said upper mold element mounted therein; tire centering meansmounted within said lower shell comprising spaced apart plates adaptedto be engaged and disengaged with bead portions of said tire; means toinflate said tire within said chamber and within said molds and toexpand said tread area of said tire against said molds; fluid exhaustmeans associated with said molds and with at least one of said shells topermit removal of fluid from within said molds while said tire is beinginflated therein, thereby insuring substantially solid contact of thetread stock on said tire with the shaping portions of said molds, andmeans for pressurizing the area exterior of said tire.